Coherent Rotation and Effective Anisotropy

It is shown in this paper that the concept of effective anisotropy is of sound physical sense only when the nucleation mode is coherent rotation. Comparison of coherent and incoherent nucleation fields demonstrates that the coherent rotation can take place at very small defect size. The critical size below which the coherent rotation is favorable is roughly the domain wall-width with 3-D soft defects and is smaller for oriented exchange-coupled permanent magnets with planar soft defects. The effect of misaligned grains has also been considered and it is illustrated that the effective anisotropy has to be used very carefully: it can only be used in limited cases and its expression varies as the microstructures change